Field of the Invention
The present invention relates to a vibration drive device including a vibration actuator and a controller for the vibration actuator, and an image pickup apparatus, and more particularly to a control technique for generating a click feeling when the vibration actuator is manually operated.
Description of the Related Art
In recent years, image pickup apparatuses, such as a digital camera, include one having a manually operable ring member which is provided around a lens barrel so as to make it possible to change the settings of photographing conditions and the like. This ring member is provided with a mechanism for generating a click feeling. This enables an operator (user) manually operating the ring member to recognize the number of steps the operator has gone through for changing a setting, based on the tactile sense of the operator's finger.
As the mechanism for providing a click feeling for the ring member, for example, there has been known a mechanism that generates a click feeling by bringing a click plate and a click ball into contact with each other. However, generally, this mechanism causes a click feeling to be generated at fixed intervals, and hence the operator is sometimes required to rotate the ring member through a plurality of turns, depending on an operation mode or type of a parameter to be set, which is not user-friendly.
To solve this problem, there has been proposed an operation ring that is capable of changing the setting of whether or not to generate a click feeling and/or the generation interval depending on the operation mode or parameter desired to be set (see e.g. Japanese Patent Laid-Open Publication No. 2013-101306). Further, there has been proposed an operation unit having a configuration for providing a click feeling for a user interface, using an actuator, for an electronic apparatus (digital camera) (see e.g. Japanese Patent Laid-Open Publication No. 2012-155674).
In the technique described in Japanese Patent Laid-Open Publication No. 2013-101306, load on the operation ring is changed by a load controller using a piezoelectric element to thereby generate a click feeling. Therefore, it is impossible to cause an operator to feel a sense as if the operation ring is drawn into a location where a click is generated. Further, there is a problem that the operation ring stops at a location where the operator releases the operator's hand from the operation ring, and hence the operation ring does not necessarily stop at a preset position.
On the other hand, in the technique described in Japanese Patent Laid-Open Publication No. 2012-155674, a click feeling is generated by controlling a DC motor using an angle detector and a torque detector, and hence it is possible to properly generate a click feeling. However, the torque detector is required to be used, which increases the number of components, so that the weight of the image pickup apparatus is increased, and further, the costs are also increased.
Further, Japanese Patent Laid-Open Publication No. 2010-257052 describes a vibration drive device (rotary input device) including a vibration actuator (ultrasonic motor). However, this vibration drive device suffers from the following problems:
In a case where the operator manually operates a rotary operation element driven by the vibration actuator, when the vibration actuator is in a non-driven state, the vibration actuator starts rotation only after the manual operation force exceeds a static friction torque generated by friction between a stator and a rotor in pressure contact with each other. Therefore, a large operation force is required, and what is more, a smooth operation feeling cannot be obtained. Further, an operation force exceeding a motion friction torque is also required during rotating operation thereof, and hence it is not easy to operate the rotary operation element. On the other hand, if the frictional force between the stator and rotor is set to a small value, a force causing a sense as if the rotary operation element is drawn into a desired location is so small that a sufficient reaction force cannot be felt.
Furthermore, there is a problem that when the direction of rotational force is switched between a normal direction and a reverse direction, there occurs an oscillating behavior around a desired location, which prevents the position of the rotary operation element from being set to the desired location with accuracy.